Replace vector-archiver with logarchiver (#308)

## Why

The Vector archiver leg wrote gzip NDJSON to S3 with no index or encryption. logarchiver replaces it with a Go service that seals raw logs to S3 as zstd + OpenPGP objects and indexes each object in ClickHouse (`logs.archive_index`), acking JetStream only after the object is stored and indexed.

## Changes

- Add logarchiver Deployment (`git.unkin.net/unkin/logarchiver:v0.1.0`), ConfigMap, and dedicated ServiceAccount, reusing the archiver's NATS (`log-consumer` / durable `archiver` / `ARCHIVE_SUBJECTS=logs.k8s.vault.>`), S3 (`logs-archive-s3`), ClickHouse (`clickhouse-credentials`) and `vault-ca` wiring.
- Encrypts to the `logarchive` gpg public key, fetched from the gpg engine via k8s auth (role `logging_logarchiver`, projected vault-audience token). `ack_wait` (5m) > batch `max_age` (2m) so messages aren't redelivered mid-batch.
- Add `logs.archive_index` DDL to the clickhouse-schema bootstrap Job (no TTL — outlives `logs.raw`).
- Remove the vector-archiver Helm release, values and pipeline ConfigMap.

Cross-repo: apply **terraform-vault #106** (gpg key + role/policy) before this syncs, or the pod can't fetch the public key. Sequencing: apply after #306 (already merged).

https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv
---------

Co-authored-by: benvin <neotheo@gmail.com>
Reviewed-on: #308
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

.woodpecker/vector-test.yaml

@@ -14,9 +14,9 @@ steps:
       # Transform tier + VM ingest: unit-tested transforms.
       - vector test apps/base/logging/vector/aggregator.yaml apps/base/logging/vector/aggregator-tests.yaml
       - vector test apps/base/logging/vector/vm-ingest.yaml apps/base/logging/vector/vm-ingest-tests.yaml
-      # Agent + archiver have no transforms to unit-test; validate they build.
+      # Agent has no transforms to unit-test; validate it builds. (The archiver
+      # leg is now the logarchiver service, not a Vector pipeline.)
       - vector validate --no-environment apps/base/logging/vector/agent.yaml
-      - vector validate --no-environment apps/base/logging/vector/archiver.yaml
     backend_options:
       kubernetes:
         serviceAccountName: default